In one widely-used commercial type of liquid containing and dispensing package incorporating a drainback system (DBS), a pouring spout is positioned on the neck of the container, either as part of a drip-catching apron fitment or integrally molded with the container body, and a closure in the form of a combined cap and dispensing cup is removably threadably interengaged with the periphery of the container neck or spout fitment.
For example, Krall U.S. Pat. No. 5,207,356 (incorporated herein reference) shows a plastic liquid containing and dispensing package which comprises a plastic blow molded container having a body portion which terminates at its upper end in an integrally formed dispensing portion that extends from and communicates with the body portion. The dispensing portion includes an annular wall or collar which extends around the body opening and encircles a dispensing spout connected at its lower end to the surrounding collar by a integral web portion that forms the drainback channel and catch apron. The interior surface of the collar has internal threads that cooperate with external threads on a closure in the form of a combined cap and dispensing cup. The closure includes a top wall and a depending annular sidewall skirt that has a sealing ring extending radially outwardly therefrom above the external threads on the skirt. When the cap is screwed down to closed position on the container neck collar, the sealing ring of the cap engages the upper end edge of the collar to provide a seal against leakage of the contents from the container.
Other types of removable closure seals are also typically provided with such container closures. For example, Hilaire U.S. Pat. No. 4,004,704 shows a tamper-proof plastic closure provided with an internal slirt forming a plug-type seal with the inner surface of the container neck as well as a V-shaped annular rib engaged in the upper end edge of the container neck to form a second seal. Likewise, Mumford U.S. Pat. No. 4,117,945 shows another type of child resistant safety closure in which sealing of the closure with the upper end of the container may be effected by a multiple sealing system including, in various disclosed embodiments, a resilient, fluid-impermeable sealing liner provided on the underside surface of the end wall of the closure, a continuous annular sealing rib of flexible and resilient material that engages the exterior cylindrical surface of the container neck as well as a sealing plug of resilient material that engages the internal surface of the container neck.
With such prior art DBS containers with cup/cap closures or with such child resistant safety closures, low viscosity products and pressure building products packaged in the container have the potential to leak past such sealing systems due to a number of factors. In the case of a plug-type seal on the closure, using a plastic container having an internal thread cooperating with an external thread on the plastic closure has in the past led to poor strip torque capability and leakage over time due to material creep. Providing an interference fit of the plug seal of the closure tends to push the container neck wall away from the plug, thereby reducing the effectiveness of the seal. Also, use of a plug-type seal in of itself may not provide sufficient torsional resistance in the fully closed and sealed position of the closure on the container to prevent the closure thread from stripping past the container thread under excessive, but often typical, hand applied final closure tightening force. However, plug-type seals are advantageous in that they can be used to help re-form an out-of-round container neck to a more true round condition to thereby improve centering of other concentric seals when a multiple array sealing system is provided between the closure and container.